Smooth out your green screen so that it has minimal wrinkling.
Place your first diffuse light to the right side of the green screen, positioning it about 5 feet from the screen. With your light placed, extend its height to around 6 feet and direct its light toward the screen.
Set up your second diffuse light to the left side of the green screen, positioning it 5 feet from the screen as with the first diffuse light. When placed, extend its height to around 6 feet, and direct its light to the screen as well. Directing both lights on either side of the screen will help to eliminate shadows.
Adjust both diffuse lights until you achieve a uniform lighting setup with both lights. You'll know when you've achieved this when all shadows are eliminated and there are no hot spots. If you're continually having trouble with hot spots, move the lights just a bit further away from the screen.
Place your subject about 10 feet from the green screen. You want to ensure that your subject isn't casting a shadow on your green screen, as this will be nearly impossible to key out later.
Light your subject with your key light by placing the light in front of and to the side of your subject. The height of this light will be dependent on the height of your subject. Extend the light so that it is around 1 foot taller than the subject being lit.
View the scene through your camera's viewfinder to see how your camera is interpreting the lighting and colors. If your camera is viewing any shadows or hot spots, continue to adjust your lighting until all instances are eliminated.